1. Field Of The Invention
The present invention relates to drive systems for battery-powered vehicles. More particularly, the invention relates to a battery-powered vehicle drive selectively operable in a normal drive mode or an alternative battery charging mode.
2. Description of the Prior Art
The development of practical battery-powered vehicles for everyday use has presented a number of substantial technical challenges. Particularly, it is important that the vehicle be as efficient as possible in order to extend operating range. This has made weight reduction a primary concern. Also, the vehicle must be able to operate over a wide range of speed and torque requirements.
It is known that polyphase AC induction motors have relatively high efficiencies. Such motors can be adapted with appropriate control systems to have relatively fast and accurate operation and control. An effective control system which has been used in many induction motor applications is "vector control." In these systems, actual motor conditions are typically compared with instantaneous demand signals. Error signals thus produced are processed and converted to polyphase currents needed by the motor to produce a desired torque and magnetic flux density.
No matter how efficient an electric vehicle is made, inevitably the storage batteries must be recharged. This has often required special external equipment. Thus, in order to increase the feasibility of such vehicles, it is desirable that the circuitry necessary to recharge the batteries be carried "on-board." This allows the vehicle to be recharged at virtually any location where electric power is available. Typical charging systems added to a vehicle, however, simply increase overall weight. Thus, improvements in convenience have been at the expense of weight which causes an increase in acceleration times and a reduction of vehicle range.